Problems - Set 7

Q1: Please discuss two pros and cons of using a single bus as a shared communication protocol between memory,
processor and I/O device


Q2: What is the bottleneck in the following system setup, the CPU, memory bus, or the disk
set?
• The user program continuously performs reads of 64KB blocks, and requires 2 million cycles
to process each block.
• The operating system requires 1 million cycles of overhead for each I/O operation.
• The clock rate is 3GHz.
• The maximum sustained transfer rate of the memory bus is 640MB/sec
• The read/write bandwidth of the disk controller and the disk drives is 64MB/sec, disk average
seek plus rotational latency is 9ms.
• There are 20 disks attached to the bus each with its own controller. (Assume that each disk
can be controlled independently and ignore disk conflicts.)


Q3: Suppose there is a processing unit composed by CPU and I/O component. For a specific task, CPU takes 5
second to finish the execution and I/O takes 2 second to process. The communication time between CPU and I/O
can be elimiate under this circumstance.
Execution Time 7 second
CPU time 5second
I/O time 2 second
If CPU time decreases by 30% per year for 3 years and I/O time decreases by 10% per year
1) How many times faster is this program after 3 years?
2) What percentage of new time is I/O? and what percentage of new time is CPU?


Q4: Disk controllers map logical blocks to physical locations on the disk.
Suppose that a 1MB file consisting of 512-byte logical blocks is stored on a disk drive with the following
characteristics:

Rotational rate: 10,000 RPM
Average seek time: 5ms
Average sectors/track: 1024
Surfaces: 4
Sector size: 512 bytes

Suppose that a program reads all the blocks of this file sequentially, and that the time to position the head over the
first block is the average seek time plus the average rotational latency.
4a) What is the best case for mapping logical blocks to disk sectors? Estimate the time required to read the file in this
best-case scenario.
4b) Suppose that the logical blocks are mapped randomly to disk sectors. Estimate the time required to read the file
in this scenario